Development of three-dimensional optimization of a small-scale radial turbine for solar powered Brayton cycle application

Numerical simulation was carried out to optimize the design of a small-scale radial turbine. One-dimensional (1D) Mean Line (ML) approach and three-dimensional computational fluid dynamic (3D CFD) simulations, using 3D Reynolds-Averaged Navier-Stokes (RANS) models with the shear stress transport (SST) turbulence model in ANSYS®15-CFX, were employed to achieve the best turbine performance and consequently cycle efficiency. For the current study, a new methodology that integrates the Brayton cycle analysis with modelling of a highly efficient small-scale radial turbine at a wide range of inlet temperatures was developed. A multi-objective function was utilized for optimizing the designed radial turbine power in the range of 1.5-7.5 kW. This method has been developed in order to find the optimum design, from an aerodynamic point of view. After applying a well-designed range of parameters for both the stator and the rotor, the results demonstrated an excellent improvement in the turbine efficiency from 82.3% to 89.7% for the same range of output power. Moreover, the effect of the turbine inlet temperature, rotational speed and pressure ratio was further studied and presented in this paper. Finally, the overall cycle efficiency showed an excellent improvement of about 6.5% for the current boundary conditions; and it yielded more than 10% with the increase in the inlet temperature and the pressure ratio. Such results highlight the potential and the benefits of the suggested methodology to achieve a high performance (i.e. turbine efficiency and cycle efficiency).